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Old 09-08-2013, 20:12   #1
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Engine Intake Size?

Hi,

I am in the process of swapping out my thru hulls and I finally got around to the engine intake thru hull. I was quite surprised to find a 3/4" intake. I would have thought at least a 1 inch or higher to make it easier on the pump.

The intake sits about 10 feet from the engine, so there is probably 15 feet or so of hose it needs to travel through.

Its a westerbeke 46...

Question is: should I increase the size of the thru hull to make it easier for the engine to perform its job?

Also, while I am at it I am thinking of adding a three way valve with the third hose going into the bilge to be able to use the engine as an emergency bilge pump. Any opinions on that?
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Old 09-08-2013, 21:39   #2
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Re: Engine Intake Size?

Back when they built my boat, they used 3'4" thru hull for the engine cooling. All of the boats had insufficient water supply. Problem solved by increase to 1". I have had to cut my feed hose once while taking water on offshore. Def will have a three way on my current boat when she hits the water.
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Old 10-08-2013, 12:28   #3
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Re: Engine Intake Size?

Quote:
Originally Posted by zboss View Post
...Question is: should I increase the size of the thru hull to make it easier for the engine to perform its job?

Also, while I am at it I am thinking of adding a three way valve with the third hose going into the bilge to be able to use the engine as an emergency bilge pump. Any opinions on that?
Check the installation manual (online) it should state the recommended size. My Westerbeke 30B3 uses 3/4 as well.

Engine as emergency bilge pump >>> IMHO this is a waste of time and false sense of security. The engine pulls little water, and in an emergency there could be all sorts of debris in the bilge - the intake gets blocked, engine overheats, now you have a leak and no engine...
Get a big Edson manual portable pump for piece of mind.

3-way Valve - Be careful what you use the other hoses, as they will be shared by the engine, you don't want to use it much while the engine is on.
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Old 10-08-2013, 19:51   #4
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Re: Engine Intake Size?

The three way valve would select between the thru hull and an internal bilge hose. I suppose I could put a strainer in the line.

I hear what you are saying about the clogged engine but if we were in serious enough doo doo to require the use of the engine for a third/fourth auxiliary pump, then not having it would probably result in a lost vessel, so the engine getting clogged wouldn't really matter.
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Old 10-08-2013, 19:59   #5
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Your engine alternator can supply power to run 5 bilge pumps any one of which can pump more water than the engine raw water pump. It is easy to over estimate the capacity of engine pumps. Check your pump specifications to be sure.

Some owners install trash pumps on a PTO or the main drive shaft. This can work.
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Old 10-08-2013, 21:24   #6
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Re: Engine Intake Size?

I'm a big believer in having the ability to pump the bilge with the engine cooling pump. Put in all of the electric, belt driven, and crash pumps you can fit and afford. Then make it easy to use your engine cooling pump as well. It costs almost nothing to do and even on the smallest engine pumps it will add another 400 or so gallons per hour to your pumping capacity. If the water goes through your sea strainer before it goes to the engine, there is no more danger of hurting your engine that you have of sucking up a plastic bag from overboard.

I'm not a big believer in manual pumps unless you have crew to spare.
Who ever is working the pump is not available to help stop the flooding.

Pumps are there to buy you time to deal with the leak. The more pumps you have, the more time you have.

This discussion is coming up almost as often as guns and anchors!
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Old 10-08-2013, 21:36   #7
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Re: Engine Intake Size?

400 gals per hour, about 6.5 gals per min. (6.66 actually) Put a bucket under your exhaust and time how long it takes to catch 6.5 gals.
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Old 10-08-2013, 22:12   #8
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Re: Engine Intake Size?

We have a 1" engine intake but we have this kind of strainer. Seems to me this is pretty restrictive. I'm going to change it out larger slotted one.
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Old 11-08-2013, 20:21   #9
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Re: Engine Intake Size?

Hi Deepfrz, I got my number from looking at the rated capacities of typical Jabsco rubber impeller pumps that might be used on a small sailboat engine.

I think 400 GPH is pretty conservative. The following is from the Jabsco website.
10950 Flange Mount 3/4" Pump
Engine Cooling Pump
Flow rate: Nominal 40 Litres/min (8.9 gallons/min) at 1500rpm
Self-priming from dry up to 2.4m (7.8ft)
Model No.: 10950-2401


Here's another 3/4" Pump.
3890 3/4" Pedestal Pump
Flow rate: Nominal 40 Litres/min (10.6 gallons/min) at 1500rpm

Other pumps might move less water depending on what the engine manufacturers want. In fact the same pumps can be made to pump less just by putting a thinner cam in them. In other works, your mileage may vary.
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Old 12-08-2013, 06:21   #10
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Re: Engine Intake Size?

Quote:
Originally Posted by HopCar View Post
Hi Deepfrz, I got my number from looking at the rated capacities of typical Jabsco rubber impeller pumps that might be used on a small sailboat engine.

I think 400 GPH is pretty conservative. The following is from the Jabsco website.
10950 Flange Mount 3/4" Pump
Engine Cooling Pump
Flow rate: Nominal 40 Litres/min (8.9 gallons/min) at 1500rpm
Self-priming from dry up to 2.4m (7.8ft)
Model No.: 10950-2401


Here's another 3/4" Pump.
3890 3/4" Pedestal Pump
Flow rate: Nominal 40 Litres/min (10.6 gallons/min) at 1500rpm

Other pumps might move less water depending on what the engine manufacturers want. In fact the same pumps can be made to pump less just by putting a thinner cam in them. In other works, your mileage may vary.
This actually speaks to the heart of both my questions. If the rated capacity of the pump is X how much capacity am I losing on a 3/4" intake going x distance? Is it possible to run my engine closer to WOT if I had a larger intake and thus more cooling capacity?
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Old 12-08-2013, 09:09   #11
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Re: Engine Intake Size?

"Is it possible to run my engine closer to WOT if I had a larger intake and thus more cooling capacity?"

What happens if you try to run at WOT now?
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Old 12-08-2013, 09:27   #12
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Re: Engine Intake Size?

The engine overheats. Its a combination of factors including a higher pitch prop than was recommended (getting repitched), a raw water pump (getting replaced), and a heat exchanger (getting replaced), etc.

While I am under the hood, I also noted the small intake which got me to wondering if the raw water pump is working harder than it needs to, thus reducing its life and causing more maintenance issues than usual.
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Old 12-08-2013, 09:50   #13
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Re: Engine Intake Size?

Jabsco gives the following general rules for guidance:

Suction pipe bore must not be smaller than the pump inlet port.
If the suction pipe exceeds 3 metres in length, its bore should be one size larger
– particularly if the pump is operated at high speeds. Use pipe of the same bore throughout. Avoid sudden changes in pipe bore. Use long, tapered sections of pipe at any change in pipe bore.

The suction pipe run should be as straight as possible – avoid unnecessary bends. Do not use square or standard elbows, but fit long swept bends.

Seacocks should be of the ball or plug type and of the same nominal bore as the suction pipework, giving full through-bore in the open position. The handle position should clearly indicate whether the seacock is open or closed.

Seawater inlet strainers should have a hole or mesh size no smaller than 3mm in diameter – or 4-5mm for larger pumps. The hole or mesh size should always be smaller than the heat exchanger tube bore.
Check frequently that the inlet strainer is not clogged. If in doubt, clean it thoroughly.

About Bronze Engine Cooling Pumps / Advice & Support / Xylem JabscoShop - Jabsco & Rule Pumps and more - from the experts
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Old 12-08-2013, 10:04   #14
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Re: Engine Intake Size?

What size is the pump? If it's a 1" or larger pump, yes change the intake system.
If it's 3/4" or smaller, changing to a intake will probably not make much difference.

You say your replacing the pump and heat exchanger, see what happens after you do that and before you spend money changing thru-hulls and seacocks.

You should of course make sure there is no restriction or blockage in the intake system.
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Old 12-08-2013, 12:42   #15
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Re: Engine Intake Size?

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What size is the pump? If it's a 1" or larger pump, yes change the intake system.
If it's 3/4" or smaller, changing to a intake will probably not make much difference.

You say your replacing the pump and heat exchanger, see what happens after you do that and before you spend money changing thru-hulls and seacocks.

You should of course make sure there is no restriction or blockage in the intake system.
The boat is already on the hard and I am replacing all the thru hulls replaced (they are original and the boat has problems with the galvanic corrosion due to what we suspect is a bad charger), so it makes sense to do it now.
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